Schools do more to help prevent obesity among children than they do to cause it, new research suggests. A nationwide study found that one measure of obesity rose more than twice as fast when kindergarten and first-grade students were on summer vacation than when they were in school.
And obese children were helped most by being in school: they gained weight no faster than other children did during the school year. It was only during the summer that overweight children gained weight more quickly than average.
"We really can't blame schools for the rise in childhood obesity," said Paul von Hippel, co-author of the study and research statistician in sociology at Ohio State University.
"The problem is primarily outside of schools."
The study comes at a time when states are putting increasing pressure on schools to help battle the epidemic of childhood obesity.
As of last August, the University of Baltimore Obesity Initiative reported 32 states had enacted or proposed legislation regulating vending machines at schools, such as prohibiting certain types of high-fat and high-sugar foods from being sold. At the same time, 37 states have enacted or proposed laws controlling the types of foods and beverages offered during school hours.
While these laws may be helpful and well-intentioned, their impact may be limited, said Douglas Downey, another co-author of the study and professor of sociology at Ohio State.
"When it comes to childhood obesity, schools appear to be more a part of the solution than the problem," Downey said. "The problem of childhood obesity would actually be much worse if children were not in school."
The study appears in the April 2007 issue of the American Journal of Public Health. It used data from a survey of 5,380 students from around the country administered by the U.S. Department of Education.
All the students were assessed for their body mass index (BMI), which is a measure of relative obesity that is derived from height and weight. The students' BMI scores were measured at the beginning and end of their kindergarten and first-grade school years. By comparing BMI scores at the end of kindergarten and the beginning of first grade, the researchers were able to assess BMI changes during summer vacation.
The study found that increases in BMI scores grew more than three times faster during the summer as they did during the kindergarten school year, and more than twice as fast as during the first-grade school year.
And it was not just overweight children who did better when they were in school. The results showed that underweight children tended to gain BMI more quickly than their peers did during the school year and more slowly during summer vacation. Meanwhile, obese children benefited the most from attending school as their rate of BMI gain was reduced the most.
In addition, schools seem to help hold the line in racial and ethnic gaps in obesity. Other studies have shown that Black and Hispanic children are most at risk for obesity, and this study confirms that finding. On the first day of kindergarten, Black and Hispanic children already showed slightly higher BMI scores than white children.
But the study showed that the racial and ethnic gaps in BMI scores only grew during summer vacation and not during the school year.
"Schools are a great treatment. They have benefits for all children, and especially for children who need it the most," Downey said.
Schools probably help limit the spread of obesity because of their structured environment, von Hippel and Downey said. Time spent in class means children's access to food is restricted. The results are consistent with earlier studies suggesting that adults, too, eat more healthily in more structured environments. Adults consume less and gain weight more slowly during the workweek than they do during the weekend or during the winter holidays.
The results don't mean that schools can't do a better job, von Hippel said.
"Schools can ensure that they have healthier choices available in vending machines and continue to improve the nutrition values of lunches," von Hippel said. "But we shouldn't be surprised if these changes have a relatively small impact on childhood obesity. The major part of the problem is outside school."
Schools may play a more important role by teaching children how to make healthier choices outside of school, such as limiting portion sizes, favoring healthy snacks, and playing kickball instead of video games.
"We need to change children's behavior after the bell rings at the end of the school day. And that means changing the out-of-school environment or the way that families respond to it," von Hippel said.